TealSignTest calls vanilla method instead of API implementation

[a6tumn]

*Issue opened as requested by ModMuss in mod-dev-kotlin channel on Discord

In the TealSignTest file, WoodType.register(...) is called to register the custom WoodType instead of Fabric's own WoodTypeBuilder.register(...), this might confuse modders who use the test mods as examples as the register(...) method is actually private in the vanilla WoodType class and is not directly callable outside of the API environment. My recommendation would be to use the API method instead so that modders who reference this file will understand what they need to do in order to register a custom wood type.